setup pkgup GH actions workflow

[jangorecki]

This uses https://github.com/jangorecki/pkgup template for simple and yet artifact rich GH Action release pipeline. Requires setting of Pages to Github Actions, rather than gh-pages branch, as most likely is set now..
Once merged we should update CI documentation in .ci/README.md. I feel it is already outdated.

[MichaelChirico]

@jangorecki @tdhock any thoughts on reviewing this now to make sure all the pending PRs have proper CI?

I lean yes but it's slightly less trivial +"no code" than the other PRs I'm reviewing now, want to double-check first.

[MichaelChirico]

Also @jangorecki PTAL at #5632 which is closely related.

[jangorecki]

If we leave GLCI then we need to move our pkgdown website to GHCI as well, but that is not a blocker. Having dev pkg being released somewhere that update_dev_pkg can use is a blocker, so that we can update url already in patch release 1.14.10..
We can merge this PR for the moment, and after 1.14.10 work on adding pkgdown, and setting redirection from r-datatable.com to GH page.

[jangorecki]

In settings-pages I have switched github pages to be deployed from GH actions rather than gh-pages git branch.

PR is ready to merge, after merging we can try out #5719
Once in master it will be able to deploy to pages

[MichaelChirico]

At a glance one might confuse pkgdown/pkgup as being closely related, maybe rename this workflow e.g. 'upload-pkg-binary'?

[jangorecki]

this is pkg sources only, and pkgup stands for putting a package up. I will document CI once we finish releasing to CRAN, so it will be clear.

[MichaelChirico]

change to 'pkgup' naming is not required, Approving now if you want to skip that. O/w will re-approve on update.